As an electrode substrate for a fuel cell of low electric resistance, there has been known an electrode plate for a fuel cell constituted with a material mainly comprising carbon fibers and having a plurality of gas diffusing pores, in which a thin-walled portion formed as a plate-like member functions as a flow channel for a fuel and an oxidizing gas while a thick-walled portion functions as a collector portion, wherein the carbon fibers constituting the collector portion comprise mono-filaments dependent on each other with the fiber axis thereof substantially oriented along the direction of the thickness of the thick-walled portion (Japanese Patent Laid Open No. Sho 57-210571). As an example for the manufacturing method thereof, the following method is disclosed. An aqueous dispersion containing carbon fibers having a length longer than the thickness of the collector portion properly dispersed therein is prepared, which is subjected to filtering operation by way of filters made of a stainless steel metal wire gauze of about 150 mesh and the carbon fibers are settled on the filters to form a mat-like carbon fibers. Upon filtering operation, if the filtering speed is increased by using a vacuum pump, the carbon fibers settled in a mat-like shape on the filters are oriented along the direction of filtration. The mat-like carbon fibers are impregnated with a binder, for example, a phenol resin, are formed with gas flow channels by hot pressing and, subsequently, they are calcined for carbonizing the binder.
In this method, however, the mat-like carbon fibers are liable to become inhomogenous and it is extremely difficult to manufacture an electrode plate of uniform physical property. This results in a serious problem, in particular, for manufacturing a substrate of large size. In addition, the strength of the electrode plate of such a structure is low at the boundary between the thick-walled portion and the thin-walled portion and it is easily broken.
As a method of fabricating a ribbed porous carbon material, there has been known a method of supplying a dry mixture comprising 20 to 50% by weight of a thermosetting resin and 80 to 50% by weight of carbon fibers in such a predetermined amount as to provide a desired porosity into a molding die in a mirror image relationship with the rib pattern desired in the substrate, press molding and then calcining the same (U.S. Pat. No. 4,165,349). Further, there has also been known a method of manufacturing an electrode substrate for a fuel cell having a large porosity and a pore diameter with a sharp distribution, by mixing carbon fibers, a binder and an organic particulate material, press molding them by pressing or rolling, followed by calcination (Japanese Patent Laid Open No. Sho 58-117649).
In this method, however, the starting material tends to be supplied unevenly to the molding die or the roll thus tending to make the physical property of the resultant substrate not uniform.
Furthermore, there has also been known a method of manufacturing an electrode substrate having a uniform physical property by extruding a starting mixture comprising short carbon fibers, a phenolic resin and a molding aid, press molding the same by means of rolling or stamping and then calcining the same (Japanese Patent Laid Open No. Sho 63-21753).
However, even the porous carbon material manufactured by such a method can not completely satisfy the physical property such as electric resistance, heat conductivity and strength required in the field of the fuel cell and a further improvement has been demanded.
It is required for the ribbed porous electrode substrate for used in a fuel cell that the electric conductivity and the thermal conductivity, in particular, those along the direction of the thickness of the substrate is high and the thickness is reduced in order to increase the power generation capacity per unit volume of a cell and reduce cost for the power generation, and it is necessary to have a sufficient strength not to be broken upon handling during assembling of a cell stack or fabrication of the substrate even if it is thin.
An object of the present invention is to provide a flat plate-like ribbed porous carbon material of great strength, as well as a manufacturing method therefor.
Another object of the present invention is to provide a ribbed porous carbon material with high electric conductivity and thermal conductivity along the direction of the thickness, as well as a manufacturing method therefor.
A further object of the present invention is to provide a ribbed porous carbon material of highly uniform physical property, as well as a manufacturing method therefor.